Q&A / 

Vapor Barrier on Foundation Walls

Quick Column Summary:

  • Tar paper or 6 mil plastic vapor barrier
  • Leave an air gap to avoid mold
  • Video link

Charles Gregoire is perplexed up in Ottawa, the capital of Canada.

"Confusion on whether to use tar paper or 6 mil plastic. In repairing a 64" section of an existing basement interior wood framed dry walled wall I discovered tar paper was glued onto the concrete wall, followed by a 1/2" gap, 2x3 wood framing followed by clear plastic vapor barrier and drywall.

Here's Charles' wall.

Here's Charles' wall.

After ripping everything out I needed to restore the section of wall. Note that there was concern over damage/mould from a plumbing leak that occurred 3 years prior. After ripping the section out I concluded there really wasn't any issue.

The fiberglass insulation was a slightly damp to the touch. I ran into some confusion when try to decide how to restore the wall section. After watching many videos and talking to people at Home Depot and Lowe's I never gain an in site into what I should do.

The fellow at Lowe's said to cover the concrete with  PE instead of tar paper. The fellow at Home Depot said that was a bad ideas because the concrete needs to "breath" and that I should use tar paper although I think he would have preferred I attach the tar paper to the back of the stud wall instead of gluing it to the concrete. I left to conclude that Tar Paper although waterproof still allowed for the passage of air whereas plastic vapor barrier would be water and air proof potentially trapping water allow for eventual mould growth. What is correct here and why?"

Here's my answer to Charles:

Charles, the fellow at Home Depot was on the right track.

Watch this video of mine about basement remodeling. I didn't have time in the video to explain the second reason you need the air gap between the back of the studs and the concrete wall. It's to allow air circulation.

I NEVER put any membrane on the concrete wall because I never wanted to TRAP moisture that would lead to mold growth.

With the 1-inch air gap, there seemed to always be enough air circulation from the top gap to prevent liquid water from forming on the concrete wall.



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